What happened
On December 26, 1971, at 08:36 GMT, a Swissair Douglas DC 9, registration HB-IFR, was performing its takeoff roll on Runway 30 at Vienna-Schwelight airport. At the time, the Runway Visual Range (RVR) was reported at 300 meters due to fog. During the acceleration phase, the crew of the DC 9 suddenly encountered a Beechcraft 55, registration HB-GCY, positioned on the runway near the intersection of taxiway Charly.
The captain of the DC 9 attempted an instinctive rotation to lift the aircraft over the obstacle, reaching speeds of approximately 115–120 knots, which was below the required takeoff speed of 141 knots. The heavy aircraft overran the light aircraft, causing a massive impact that resulted in the destruction of the Beechcraft 55 and the death of its pilot. The DC 9 crew successfully aborted the takeoff, utilizing reverse thrust and braking to bring the aircraft to a halt. Following the collision, a small fire broke out near the left landing gear of the DC 9, necessitating an emergency evacuation of the 74 passengers and crew via the right-side emergency slide. Two passengers on the DC 9 sustained minor injuries.
The investigation
The investigation examined the sequence of events, the visibility conditions, and the communications between the aircraft and ground control. Investigators reviewed the cockpit voice recordings and analyzed the runway visibility measurements. The inquiry also looked into the technical status of both aircraft and the maintenance records of the Beechcraft 55, noting that certain scheduled maintenance inspections had been delayed by the pilot. The investigation focused on the interaction between the air traffic controllers and the pilots during the takeoff clearance process under low-visibility conditions.
Findings
- The primary cause of the collision was the presence of the Beechcraft 55 on the active runway during the takeoff roll of the DC 9.
- Low visibility (300m RVR) significantly hindered the ability of the flight crew to visually identify the obstacle on the runway until it was too late to avoid the collision.
- There were potential ambiguities in radio telephony phraseology, specifically regarding the use of "cleared into position" versus "cleared to line up," which could lead to confusion regarding the aircraft's exact location.
- The maintenance of the Beechcraft 55 was not up to date, as the pilot had exceeded several maintenance intervals.
Safety action
- Recommendations were made to ensure that aircraft are cleared to taxi only to the runway threshold, especially during poor visibility.
- The use of follow-me vehicles was suggested for aircraft taxiing on taxiways when visibility is insufficient for the tower to monitor the movement area effectively.
- It was recommended that air traffic controllers receive enhanced training regarding the precise use of radio phraseology to prevent misunderstandings.
- The investigation suggested improving the RVR monitoring system through the use of automated recording equipment.